M252: Support configurability of USB/STDIO UART pins

-   STDIO_UART and STDIO_UART_TX/STDIO_UART_RX
-   USB_UART and USBTX/USBRX

targets/TARGET_NUVOTON/TARGET_M251/PeripheralNames.h

@@ -20,6 +20,7 @@
 #define MBED_PERIPHERALNAMES_H
 
 #include "cmsis.h"
+#include "PinNames.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -77,7 +78,16 @@ typedef enum {
     UART_2 = (int) NU_MODNAME(UART2_BASE, 2, 0),
 
     /* NOTE: board-specific */
-    STDIO_UART  = UART_0
+#if defined(MBED_CONF_TARGET_USB_UART)
+    USB_UART    = MBED_CONF_TARGET_USB_UART,
+#else
+    USB_UART    = NC,
+#endif
+#if defined(MBED_CONF_TARGET_STDIO_UART)
+    STDIO_UART  = MBED_CONF_TARGET_STDIO_UART
+#else
+    STDIO_UART  = USB_UART
+#endif
 } UARTName;
 
 typedef enum {

targets/TARGET_NUVOTON/TARGET_M251/PinNames.h

@@ -70,7 +70,7 @@ typedef enum {
 typedef enum {
     /* Not connected */
     NC = (int)0xFFFFFFFF,
-    
+
     /* Generic naming */
     PA_0    = NU_PINNAME(0, 0), PA_1, PA_2, PA_3, PA_4, PA_5, PA_6, PA_7, PA_8, PA_9, PA_10, PA_11, PA_12, PA_13, PA_14, PA_15,
     PB_0    = NU_PINNAME(1, 0), PB_1, PB_2, PB_3, PB_4, PB_5, PB_6, PB_7, PB_8, PB_9, PB_10, PB_11, PB_12, PB_13, PB_14, PB_15,
@@ -103,21 +103,37 @@ typedef enum {
     D13 = PA_2,
     D14 = PC_0,
     D15 = PC_1,
-    
+
     /* Other board-specific naming */
-    
+
     /* UART naming */
-    USBTX = PB_13,
-    USBRX = PB_12,
+#if defined(MBED_CONF_TARGET_USB_UART_TX)
+    USBTX           = MBED_CONF_TARGET_USB_UART_TX,
+#else
+    USBTX           = NC,
+#endif
+#if defined(MBED_CONF_TARGET_USB_UART_RX)
+    USBRX           = MBED_CONF_TARGET_USB_UART_RX,
+#else
+    USBRX           = NC,
+#endif
+#if defined(MBED_CONF_TARGET_STDIO_UART_TX)
+    STDIO_UART_TX   = MBED_CONF_TARGET_STDIO_UART_TX,
+#else
     STDIO_UART_TX   = USBTX,
+#endif
+#if defined(MBED_CONF_TARGET_STDIO_UART_RX)
+    STDIO_UART_RX   = MBED_CONF_TARGET_STDIO_UART_RX,
+#else
     STDIO_UART_RX   = USBRX,
+#endif
     SERIAL_TX       = D10,
     SERIAL_RX       = D13,
 
     /* I2C naming */
     I2C_SCL = D15,
     I2C_SDA = D14,
-    
+
     /* LED naming */
     LED_RED = PB_14,
     LED1    = LED_RED,
@@ -126,7 +142,7 @@ typedef enum {
     LED4    = LED1,     // No real LED. Just for passing ATS.
 
     /* Button naming */
-    
+
     /* Force PinName to 32-bit required by NU_PINNAME_BIND(...) */
     FORCE_ENUM_PINNAME_32BIT = 0x7FFFFFFF,
 

targets/targets.json

@@ -5656,6 +5656,30 @@
             "IAR"
         ],
         "config": {
+            "usb-uart": {
+                "help": "Configure USB_UART. USB_UART and USB_UART_TX/USB_UART_RX must be consistent.",
+                "value": null
+            },
+            "usb-uart-tx": {
+                "help": "Configure USBTX. USB_UART and USBTX/USBRX must be consistent.",
+                "value": null
+            },
+            "usb-uart-rx": {
+                "help": "Configure USBRX. USB_UART and USBTX/USBRX must be consistent.",
+                "value": null
+            },
+            "stdio-uart": {
+                "help": "Configure STDIO_UART. STDIO_UART and STDIO_UART_TX/STDIO_UART_RX must be consistent. STDIO_UART defaults to USB_UART.",
+                "value": null
+            },
+            "stdio-uart-tx": {
+                "help": "Configure STDIO_UART_TX. STDIO_UART and STDIO_UART_TX/STDIO_UART_RX must be consistent. STDIO_UART_TX defaults to USBTX.",
+                "value": null
+            },
+            "stdio-uart-rx": {
+                "help": "Configure STDIO_UART_RX. STDIO_UART and STDIO_UART_TX/STDIO_UART_RX must be consistent. STDIO_UART_RX defaults to USBRX.",
+                "value": null
+            },
             "gpio-irq-debounce-enable": {
                 "help": "Enable GPIO IRQ debounce",
                 "value": 0
@@ -5733,7 +5757,12 @@
             "2",
             "5"
         ],
-        "device_name": "M252KG6AE"
+        "device_name": "M252KG6AE",
+        "overrides": {
+            "usb-uart": "UART_0",
+            "usb-uart-tx": "PB_13",
+            "usb-uart-rx": "PB_12"
+        }
     },
     "TMPM4G9": {
         "inherits": [